1. Field of Invention
The present invention relates to an evaporation system. More particularly, the present invention relates to a supplier of evaporation source material.
2. Description of Related Art
Thin film deposition technique includes physical vapor deposition and chemical vapor deposition. Physical vapor deposition includes evaporation deposition. Evaporation deposition is carried out by heating an evaporation source to vaporize the source material. The vaporized material forms a saturated vapor that can be deposited back onto a cooler surface as a thin film. Most evaporation system includes an evaporation chamber and a vacuum system for creating a vacuum inside the evaporation chamber. The evaporation chamber also contains an evaporation boat and a wafer holder. The evaporation boat is a container for holding evaporation material normally positioned at the lower end of the evaporation chamber. The evaporation boat can be made from a substance having a high melting point. There is a wafer holder near the top end of the evaporation chamber. The wafer holder is a device for holding a wafer or a substrate that requires thin film deposition. When a suitable current runs through the evaporation boat, the evaporation boat is heated up due to resistor effect. The source material will be heated to a temperature close to its melting point. At such a high temperature, the source material starts to evaporate and saturate the evaporation chamber. The evaporated source particles are deposited onto the cooler wafer surface, thus initiating the thin film deposition process.
FIG. 1 is schematic front view of a conventional evaporation system. As shown in FIG. 1, the evaporation system 100 includes an evaporation chamber 102 and a vacuum extraction system 104. The vacuum extraction system 104 is connected to the evaporation chamber 102. The components inside the evaporation chamber 102 include an evaporation boat 106 and a wafer holder 108. The evaporation boat 106 is in the lower portion of the evaporation chamber 102 for holding an evaporation source 110. The wafer holder 108 is in the upper portion of the evaporation chamber 102. The wafer holder 108 is a device for holding a wafer 112 requiring thin film deposition. When a suitable current runs through the evaporation boat 106, the evaporation boat 106 and the source material 110 are heated up to a temperature close to the melting point of the source material 110. At such a high temperature, the solid source material 110 evaporates into vapor that can be deposited back onto the wafer 112 lying above the evaporation source 110. However, a conventional evaporation system may run out of evaporation source material in a continuous evaporation process and need replenishing. Time is often wasted in replenishing the evaporation boat 106 because the vacuum inside the evaporation chamber needs to be retreated and then re-established after each replenishing. Thus, source material replenishing not only slows thin film deposition, but also increases operating load of the vacuum extraction system 104.
Accordingly, one object of the present invention is to provide a system capable of providing sufficient evaporation source material to last the entire course of a thin film deposition or a long-period continuous deposition. Hence, time-out due to insufficient source material can be prevented and a higher overall productivity can be achieved.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a supplier of evaporation source material. The evaporation system that uses the source material supplier includes an evaporation chamber and a vacuum extraction system. The vacuum extraction system is connected to the evaporation chamber. The source material supplier, a movable evaporation boat and a wafer holder are housed inside the evaporation chamber. The source material supplier is on one of the sidewalls of the evaporation chamber. The wafer holder is in the upper portion of the evaporation chamber. The wafer holder is responsible for holding a wafer requiring thin film deposition. The movable evaporation boat is in the lower portion of the evaporation chamber for holding evaporation source material. The source material supplier includes a revolving cassette wheel and a crucible under the cassette wheel. The revolving cassette wheel is partition by separating plates and an outer casing into a plurality of capsules with each capsule capable of holding a fixed amount of evaporation source material. When the cassette wheel rotates, the lowest capsule can deliver a lump of evaporation source material onto the crucible via a drop hole in the outer casing.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.